Garnier Belle Color

Hello, On Saturday 1st Novement 2008 I used Garnier Belle Color Natural Brown,
The roots of my hair were darker than the rest of my hair and the problem is the dye has darkened the rest of my hair to a similar colour to on the box but my roots have been lightened and look very brassy.

Can you tell me can I use this product again and will it make my hair and roots the same colour as it should darken my roots now as they are lighter than the colour stated on the box.

Please help! Thank you